1. Field of the Invention
The present invention pertains to a method for exchanging data between a first data processing unit containing first status information about the first data processing unit and a second data processing unit containing second status information about the first data processing unit. Data are exchanged between the first data processing unit and the second data processing unit during the course of transactions. The transactions include status-changing transactions, at the successful completion of which the first status information and the second status information are revised such that they match. At least two different types of status-changing transactions are carried out. The present invention also pertains to a corresponding arrangement for implementing this method.
2. Description of the Prior Art
Constellations of this type with a first data processing unit containing first status information about its status and a second data processing unit containing second status information about the status of the first data processing unit are frequently encountered in certain networks that are composed of such data processing units. In some known networks, for example, a series of first data processing units performs certain services or offers certain functions independently of a central second data processing unit. It is occasionally necessary, however, for the first data processing unit to communicate with the central second data processing unit. During the course of this communication, the utilization of the first data processing unit is acquired in the central second data processing unit by comparing the first and the second status information.
Another part of such communications frequently is in the form of transactions that change the status, in particular, the first status information of the first data processing unit.
Often the first data processing unit is locked for further use after a certain time of utilization or after a certain intensity of utilization that is indicated by the first status information. In order to cancel or prevent the locking of the first data processing unit, a status-changing transaction is carried out in which the first status information is revised in such a way that the first data processing unit can once again be used for an extended period of time or to a greater extent. In other words, a status-changing type of transaction is carried out in this case in order to broaden the privileges of the first data processing unit.
Transactions of a different type are also carried out quite frequently, wherein the privileges of the first data processing unit are restricted by these transactions. It is possible, in particular, to lock the first data processing unit for further use with such a transaction because it was detected that the data processing unit was somehow manipulated or the user of the first data processing unit is delinquent in paying the fee for utilizing the first data processing unit. One example of first data processing units in a constellation of this type are the accounting units of postage metering machines, in which the available credit balance is stored. In order to ensure the uninterrupted metering of postage, it is necessary to periodically load funds so as to refill the credit balance via a remote data center that functions as the second data processing unit, namely with a first type of transaction. If an excessively high amount of credit was loaded or the loaded amount should be reduced for other reasons, postage metering machines of this type frequently allow for lowering the credit balance with a second type of transaction.
The data center maintains records on the status of each registered postage metering machine, namely for the time at which the data center and the respective postage metering machine were last in contact. These records on the status of the postage metering machine, i.e., the second status information on the first data processing unit, are maintained in the data center so as to prevent fraud attempts in the form of manipulations of the first status information, e.g., the deposited credit balance, from remaining undetected.
During each status-changing transaction that is not successfully completed, for example, due to a premature interruption of the communication link, it remains unclear whether the first status information and the second status information were revised such that they match.
In the case of such an unsuccessful status-changing transaction, the user of the postage metering machine usually needs to repeat the corresponding procedure as many times as required for successfully completing the transaction. For the user of the postage metering machine, this is a bothersome and usually time-consuming process.
In this context, it is disclosed in U.S. Pat. No. 5,699,415 to carry out a check between the postage metering machine and the data center during the course of an ensuing transaction, wherein the check provides information as to whether the prior transaction was successfully completed. If the check indicates that the prior transaction was not successfully completed, it is suggested to repeat, cancel or patch this transaction. However, the problem encountered in this case is that an incorrect status of the postage metering machine is registered in the data center for the duration between the unsuccessfully completed transaction and the ensuing transaction.
If a deposit transaction is terminated, for example, after the second status information is revised in the data center but before the first status information is correspondingly revised in the postage metering machine, an excessively high credit balance—i.e., a debit for the user of the postage metering machine—is incorrectly registered in the data center. With regard to security aspects, this may be acceptable for the operator of the data center. If a transaction is interrupted in which the credit balance is lowered due to a return of funds, however, an excessively low credit balance in the postage metering machine, i.e., a credit for the user, is incorrectly registered in the data center. With regard to security aspects, this is undesirable for the operator of the data center because funds may be erroneously refunded, if applicable, to the user of the postage metering machine before the error is detected.
With respect to the handling of credit balances of postage metering machines, the security aspects of the operator of the data center predominate. The satisfaction of the user is of primary importance in other transactions, for example, the clearance of the postage metering machine for initial use. In this case, it would be undesirable if the postage metering machine were actually cleared for use but remained registered as being locked in the data center such that the metering processes carried out with this postage metering machine will be categorized as invalid when using the status data registered at the data center.